Scaling of Precipitation in the Alps: Insights from a Convection Permitting Regional Climate Model Ensemble

Previous studies predict an intensification of heavy precipitation events with climate change. These events are widely known to cause natural disasters with great property damage and loss of life, like flash floods or landslides. Knowledge about the scaling of precipitation, referring to the changes of precipitation intensity to warmer temperatures, is important for effective mitigation measures. Previous studies have investigated this scaling with regards to the Clausius Clapeyron relation, over various regions worldwide, using observational as well as model data. In this study we analyze the precipitation scaling over an orographically complex region as the Alps, as well as compare different methods to obtain the scaling rate.

To this end, we employ a 10-year multi-model ensemble of kilometer-scale convection-permitting climate model (CPM) simulations over the Greater Alpine Region from the CORDEX-FPS, with a spatial resolution ranging from 2.2 to 4 km. These simulations were obtained by downscaling global climate model (GCM) projections to intermediate regional climate models (RCMs), which were in turn further downscaled to kilometer scale by convection permitting climate models (CPMs). Previous work has shown the added value of these CPMs compared to lower resolution RCMs especially for extreme precipitation. We analyze these simulations over four alpine subdomains, which are characterized by different climatological characteristics.

In the calculation of precipitation scaling rates, we use two different precipitation indices, wet-hour percentiles and all-hour percentiles. These indices differ in that the latter encompasses all events, wet and dry, whereas the wet-hour percentile only includes events that go over a certain threshold. We compare the scaling calculated using these precipitation indices on an annual and seasonal basis, to show insights into the mechanisms that may cause scaling rates to exceed expectations given from the Clausius Clapeyron relation. Our results show that future precipitation intensity may be inferred from present-day scaling. The seasonal analysis shows scaling exceeding the Clausius Clapeyron scaling in the summer and autumn seasons for the wet-hour analysis, but not for the all-hour analysis.